Another important factor in determining the distance a radio can communicate is it's signal strength. The stronger the signal strength, the more it can withstand weakening when it passes through obstacles. Signal strength is mainly a result of a radios' power output, measured in watts. Commercial radio stations typically broadcast at 50,000 or 100,000 watts. Compare that to a handheld two-way radio which uses between 1/2 - 5 watts. You can see there is a big difference.
Unlicensed radios such as: FRS radios are limited to 2 watts, MURS 2 watts, CB radios 4 watts, and CB radios with SSB channels can have 12 watts on the SSB channels*. Other handheld radios such as marine, aviation, and licensed land-based radios such as: LMR, Ham, & GRMS are limited to 5 watts, again radios with SSB can have 12 watts. The maximum wattage for each radio type is set by the FCC. Moreover, handheld radios run off a small battery, so a higher wattage would mean your batteries will not last very long.
*Single side band (SSB) is used in some amateur (ham) radios, and some CB radios. One benefit of radios with SSB channels is additional power. The FCC allows 12 watts of transmit power for SSB transmissions. However, when communicating on SSB channels, both the sending and receiving radios must have SSB channels.
* Although FRS radios can have up to 2 watts, many manufacturers are still currently selling FRS radios with 1/2 watts.
These are averages. Assumes standard equipment. Antenna type can have a significant effect on range.
|Average Range Guidelines * |
|Wattage ||Flat Open |
|FRS ½ - 2 watts * ||½ - 2 ||½ - 1½ ||¼ - ½ ||3 - 5 |
|1 watt (UHF) ||2 - 3 ||1 - 2 ||½ - 1¼ ||6 - 8 |
|2 watts (UHF) ||3 - 4 ||1½ - 2½ ||1 - 1½ ||15 - 20 |
|2 watts (VHF) ||3 - 5 ||1½ - 3 ||¾ - 1 ||9 - 11 |
|4 watts (HF) ||5 - 6 ||2½ - 4½ ||1 - 3 ||10 - 15 |
|4 watts (UHF) ||4 - 6 ||2½ - 4½ ||1½ - 3 ||25 - 30 |
|5 watts (VHF) ||4½ - 6 ||2 - 4 ||1½ - 2 ||10 - 15 |
|12 watt CB SSB (HF) ||8 - 15 ||5 - 8 ||3 - 5 ||--- |
Car, Boat, & Other Radios (Mobile & Fixed-Mount)
Mobile radios usually broadcast from 25 to 100 watts maximum. Installed in vehicles, they run off the vehicle's battery. Their signal is much stronger than a handheld radio, therefore less affected by obstacles. However, their signal can still only travel to the horizon. So just having more watts without a better antenna is like having a large funnel with a small hole. So mount your antenna as high-up on your vehicle as possible. Remember the higher your antenna the father the horizon is. So more watts, along with a better antenna, equals longer range.
To sum it up, the more watts a radio has, the stronger the signal. A stronger signal is capable of withstanding successive passes through obstacles, allowing it to travel farther.